There are a total of six slots in the combat roster. There are three in front and three in back. The front three represent the characters in the front lines with you. The back three represent the reserve NPC's. Choose carefully what characters you Slot and in what Slots you Place Them. The reason for this isn't just to keep battles orderly by using as few characters as are effectively possible, but also because of a feature known as The Support System. A Support is a character's immediate effect on the characters in the Battle Roster Front Line. They are active the second a character is slotted and act passively. Many supports are Offensive. However, there are also Defensive supports so be alert. What characters in the line a character's support effects varies. But if a character's support says that it reaches the characters immediately next to them and they are in the front or back of the line, it will effect the character on the opposite end. Here is an example of the Slots.

(Player1)-Lucas-(Player2)-Lei(Player3)-(Player4)-Celcius

So, for example, Lucas is in the middle of two OC's. Say his support reaches any character immediately next to him. Immediately, Lucas' support will affect both P1 and P2. Another example. Say Lei's Support had the same range. Her support would reach the same as Lucas because P2 is beside her and P1 is on the opposite side of the chain. This only applies if the character doesn't actually have another character on one side.

Traits

In the same way that all characters have Supports, all characters also have Special Traits. Special Traits may be active in battle or off depending on the character. These are not things that your own OC's will have and is exclusive to NPC's because they are designed to help the players along in the game. Some characters have poor Supports but very useful Special Traits. All characters are in some way useful. Traits can be effective specifically in battle and some carry over into Travel-Play. But Traits are only active to the characters that are slotted.